I.2 Formatting

24.3023GPPAccess to the 3GPP Evolved Packet Core (EPC) via non-3GPP access networksRelease 17Stage 3TS

I.2.1 General

For the purposes of aiding in detection of emergency call number and assigning the emergency type, the Emergency Call Number Unit field can contain an emergency call number and one or more emergency call labels.

The emergency call number and one or more emergency call labels shall be encoded as a namespace specific string for the namespace identifier equal to 3gpp (see RFC 5279 [74]). This specification further defines the namespace identifier equal to sos-anqp and parameters.

For the purposes of aiding in determining of the country where these local emergency numbers were provided, the Emergency Call Number field contains the MCC. The MCC represents the country in which the AP is located.

I.2.2 ABNF for the urn:3gpp:sos-anqp namespace and its parameters

Table I.2.2-1 contains the ABNF (RCF 2234 [73]) for the urn:3gpp:sos-anqp namespace and its parameters.

Table I.2.2-1: Syntax of urn:3gpp:sos-anqp

emergency-information = "urn:3gpp:sos-anqp:" mcc *(":" number 1*(":" label ))

mcc = "mcc" DIGIT DIGIT (DIGIT) ; exactly 2 or 3 digits

label = "sos" *("." sub-label)

number = DIGIT*DIGIT ; at least one DIGIT

sub-label = let-dig [ *let-dig-hyp let-dig ]

let-dig-hyp = let-dig / "-"

let-dig = ALPHA / DIGIT

ALPHA = %x41-5A / %x61-7A ; A-Z / a-z

NOTE: While the syntax of table I.2.2-1 allows for many different sub-labels following "sos", when originating an emergency IMS session (see TS 24.229 [67]) based on detecting a match with dialed digits, the SIP INVITE will only contain one of the following service URNs: "urn:service:sos", "urn:service:sos.police", "urn:service:sos.ambulance", "urn:service:sos.fire", "urn:service:sos.marine", "urn:service:sos.mountain".

I.2.3 Semantics

According to the ABNF in table I.2.2-1:

– "urn:3gpp:sos-anqp:mcc310" is a valid expression: this expression indicates to the UE to overwrite any previously received list with Local WLAN emergency numbers with an empty list;

– "urn:3gpp:sos-anqp:mcc222:112:sos.police:sos.ambulance" is a valid expression: this expression indicates to the UE to that in the country with MCC 222 the number 112 is an emergency number. The corresponding labels sos.police and sos.ambulance are mapped in accordance with annex I.2.4.

I.2.4 Mapping Emergency Call Number field’s contents to the Local WLAN Emergency Numbers List

When the Local WLAN Emergency Numbers List is to be encoded in the Local Emergency Numbers List format as defined in 3GPP TS 24.008 [46], clause 10.5.3.13, the Emergency Call Number field’s contents conforming to the ABNF for the urn:3gpp:sos-anqp namespace shall be mapped. The Local WLAN Emergency Numbers List for the PLMN with which the UE is connected via WLAN shall only be used when the contents are considered valid (see clause 6.4.1).

The contents of the Emergency Call Number Unit field map to 4 bit encoded number digits and 5 bit encoded Emergency Service Category Value as follows. In addition to the rules in 3GPP TS 24.008 [46], the following mapping shall apply for a URN with UTF-8 (see RFC 3629 [34]) digits in the mcc ABNF portion that match the MCC of the PLMN with which the UE is connected via WLAN :

1) each UTF-8 digit in the emergency-number ABNF portion of the URN is converted into a corresponding 4-bit number digit of a set of octets part of an emergency number information; and

2) the label ABNF portion of the URN maps as follows:

"sos": does not set bits of the 5 bit encoded Emergency Service Category Value of the emergency number information;

"sos.police": sets bit 1 (police) of the 5 bit encoded Emergency Service Category Value of the emergency number information;

"sos.ambulance": sets bit 2 (ambulance) of the 5 bit encoded Emergency Service Category Value of the emergency number information;

"sos.fire": sets bit 3 (fire brigade) of the 5 bit encoded Emergency Service Category Value of the emergency number information;

"sos.marine": sets bit 4 (marine guard) of the 5 bit encoded Emergency Service Category Value of the emergency number information;

"sos.mountain": sets bit 5 (mountain rescue) of the 5 bit encoded Emergency Service Category Value of the emergency number information.

Annex J (normative):
Emergency Call Numbers from DNS procedure